Scaled old raids would be nice if it doesn't become the only way to raid them. A lot of people (especially those of the casual variety) enjoy running old content; it's not challenging, but it's nostalgic and/or allows newer players to get a taste of times long gone.

But eh, I doubt it would be forced upon us. They've made quite a few changes to allow players to solo old raids.

Allowing horde and ally to run raids together can cause major issues (like guilds demanding all be trolls for OP racials, or players hating/kicking other players if they are a certain race), while it provides absolutely no benefit - the amount of people in queue would double and DPS would be waiting even more for that Tank/Healer.

It will most probably be a feature allowing us to raid old raids/5man as end game content with proper rewards.

I actually think the 'unannounced feature' is just going to be ingame access to the Blizzard store. Its not that big a leap between what they've just done with the support/online help system and added a link to the Blizzard store.

A level 90 can que for ANY dungeon or heroic and their gear gets scaled down. They will be rewarded valor for completing the dungeon (as they do now for completing level 90 dungeons). This could also happen for raids. With the buff that makes raids easier over time, it will mean that if a group fails in a raid, they will become more powerful and making it easier.

SOmething simple I would like is the option to match armor colors schemes. The biggest thing preventing people from creating unique armor sets is non-matching colors. Having the ability to "unify to chest piece" or something will increase the armor you'd be comfortable transmogging to a thousand fold.

Not saying that that is THE big feature, but it feeds into running older content.